Computing and data storage based on spin1,2, resistive switching3,4 or phase change5-13 has received considerable attention as charge-based electronics approach their fundamental scaling limits, particularly due to charge leakage and power dissipation issues14. Phase change materials (PCMs) such as the chalcogenide Ge2Sb2Te5 (GST), are particularly interesting for applications in electrical/optical data storage5-13 and reconfigurable electronics15. Unlike conventional charge-based electronics, PCM devices store data as the state of the material which can be reversibly switched between a high-resistance amorphous and a conductive crystalline phase. This behavior renders them effectively immune to leakage for low-power electronics, or radiation damage for remote terrestrial or space applications. PCM switching is induced by Joule heating through voltage pulses for electrically-programmable PCMs6-13. However, such devices have historically required relatively high programming current (0.1-0.5 mA) and power (˜0.5 mW)6,7. To address this challenge, the dimensions of the programmable bit could be reduced by confining16 it into nanowires (NW)8,9,13, or by contacting it with sharp electrodes like carbon nanotubes (CNTs)10-12. NWs confine the bit in the cross-plane perpendicular to the current flow, while CNTs can contact very small bit dimensions commensurate with their ˜2-nm diameter.